Brewster is one of the calmer Route 6A towns on Cape Cod. It does not have Provincetown's theatre or Chatham's polish, but it has a good Cape mix: bay-side light, old houses, galleries, kettle ponds, and bike paths through pine woods.
The strongest reason to stop is the landscape around Nickerson State Park and the Cape Cod Museum of Natural History. Add the Stony Brook Grist Mill in herring season and Brewster becomes a good low-key day, especially by bike.
Brewster is not a place for a checklist. It is for travellers who like the quieter Cape: ponds, marshes, old windmills, and enough local history to slow the drive between bigger towns.